Method for manufacturing piezoelectric resonator

ABSTRACT

To provide a method for manufacturing a piezoelectric resonator which can conduct frequency matching with high reliability when performing rough adjustment of the frequency by adjusting the shape of a piezoelectric oscillating piece before forming an electrode film, and thereby it becomes possible to avoid reduction of the yield. Etching for forming the shape of a piezoelectric oscillating piece, and etching for forming grooves are conducted simultaneously, and after forming the grooves, the shape formation of the piezoelectric oscillating piece is started again from the same depth as the groove in a state of covering the groove with a metal film, and after the shape formation, matching of frequency is conducted by etching the side surface of the piezoelectric oscillating piece in succession. By composing such a structure, it is possible to conduct rough adjustment of frequency at a low etching rate so that the frequency matching can be performed with no due difficulty and with high accuracy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technology for manufacturing, forinstance, a tuning fork type piezoelectric resonator using apiezoelectric substrate made of, for instance, quartz crystal or thelike.

2. Description of the Related Art

The tuning fork type quartz resonator has long been adopted as a signalsource for pacing of a wrist watch owing to its compactness,inexpensiveness and low power consumption, and the uses thereof arestill expanding. The CI (crystal impedance) value of this quartzresonator is required to be as small as possible for the purpose ofreducing the power loss, and therefore a quartz resonator of whichoscillation efficiency is enhanced by forming a groove therein has beenused for this purpose.

As shown in FIG. 7, the quartz resonator is provided with a pair ofvibrating arms 2 a and 2 b in a base 1, and the grooves 31 and 32 arerespectively arranged on both main surfaces of the respective vibratingarms 2 a and 2 b. Excitation electrodes for exciting tuning forkvibration based on bending vibration are formed in these grooves 31, 32and the respective vibrating arms 2 a, 2 b.

The above-described quartz resonator is manufactured according to thefollowing process (refer to Patent Document 1). FIGS. 8A to 8E and FIGS.9F to 9I are views showing the manufacturing processes of the crosssectional portion along A-A line in FIG. 7. First, after polishing andcleaning a cutout quartz wafer 10, a metal film 11 is formed by asputtering method (FIG. 8A). A film in which gold (Au) is stacked on abacking film of, for instance, chromium (Cr) is used as the metal film11.

Then, after applying photoresist on such a metal film 11 by a spraymethod for instance (FIG. 8B), the photoresist is exposed and developedin a s manner to obtain a pattern having the shape of the quartz piece10, namely, a tuning fork shape pattern, so that a tuning fork shapedresist film 12 is formed (FIG. 8C). Thereafter, the portion of the metalfilm 11 not covered with the resist film 12 is removed by etching, andthe whole resist film 12 remaining on the quartz wafer 10 is removed(FIG. 8D).

Next, photoresist is applied to the whole surface of the quartz wafer 10by, for instance, a spray method, and the photoresist is exposed anddeveloped to form a resist film 13 (FIG. 8E). Then, the resist film 13is peeled off so that the outside shape of the quartz piece is left, andthe resist film 13 at portions corresponding to the grooves 31 and 32shown in FIG. 7 is peeled off (FIG. 9F).

Thereafter, wet etching is conducted by immersing the quartz wafer 10 inhydrofluoric acid which is an etching solution using the resist film 13as a mask to form the outside shape of the quartz piece (FIG. 9G). 14and 15 in FIGS. 9F to 9I are portions corresponding to the vibratingarms 2 a and 2 b, and 16 and 17 in FIGS. 9F to 9I are outer frameportions described for convenience of taking out a sheet of quartz piecefrom the quartz wafer. Then, wet etching is conducted by immersing thequartz wafer 10 in a potassium iodide (KI) solution using the resistfilm 13 as a mask to remove the metal film 11 at the portionscorresponding to the grooves 31 and 32 shown in FIG. 7 (FIG. 9H). Then,wet etching is performed by immersing the quartz wafer 10 inhydrofluoric acid. By these processes, the grooves 31 and 32 are formedon both main surfaces of the quartz piece 10 (FIG. 9I).

Thereafter, a frequency matching process (rough adjustment inoscillation frequency) through which matching to a prescribed frequencyis performed by reprocessing the side surfaces of the outside shape ofthe quartz piece 10 and the grooves 31, 32 by immersing the quartz wafer10 in hydrofluoric acid. The frequency matching process includesimmersing the quartz wafer 10 in hydrofluoric acid, suspending the wetetching after a predetermined period of time, cutting out a quartz piecefrom the original which is in a state of before forming an electrodepattern and forming the electrode on the quartz piece. A prescribedvoltage is applied to the electrode and the oscillation frequency f isdetected to determine whether or not the oscillation frequency f iswithin the predetermined frequency.

Thereafter, an electrode pattern is formed on the surface of the quartzpiece 10, a fine adjustment in the oscillation frequency is conducted byshaving the metal film formed on the tip portion of the vibrating arm soas to adjust the thickness thereof.

The oscillation frequency of quartz resonator is determined dependingupon the length and the width of the vibrating arms 2 a and 2 b, thelength, width and depth of the grooves 31, 32 and the like shown in FIG.7. Accordingly, in the frequency matching process before forming theabove-described electrode pattern, since the side surfaces of theoutside shape and the grooves 31, 32 of the quartz piece 10 are etchedsimultaneously, the change in frequency is very large, and it isdifficult to suspend the etching process at the most suitable pointwhere the predetermined frequency is obtained. Therefore, it has aproblem that fine frequency adjustment doesn't go well even through thefrequency adjustment process after the electrode pattern formingprocess, which reduces yields.

Patent Document 1

Japanese Patent Application Laid-open No. 2002-76806 (columns 0094 to0113, FIG. 9 to FIG. 13)

SUMMARY OF THE INVENTION

The present invention is achieved under the consideration of such acircumstance and its object is to provide a method for manufacturing apiezoelectric resonator which can perform frequency matching with highreliability when conducting rough frequency adjustment by adjusting theshape formation of a piezoelectric oscillating piece before forming anelectrode film so that the reduction in the yields can be prevented.

In the method for manufacturing a piezoelectric resonator including abase, a plurality of vibrating arms extending from the base, groovesformed in these respective vibrating arms, the present inventionincludes the steps of:

forming a metal film on the surface of the base which is a piezoelectricsubstrate;

patterning the surface of the metal film so that the outside shapeportion of the piezoelectric oscillating piece is left, forming a resistmask having apertures at the portions corresponding to the grooves ofthe vibrating arms, and removing the metal film by etching;

forming the grooves on the vibrating arms thereafter by bringing theabove-described substrate into contact with an etching solution, andforming the shape of the piezoelectric oscillating piece to the samedepth as the grooves;

thereafter, peeling off all of the metal film remaining on the substratesurface;

then forming a metal film on the substrate surface;

forming a resist mask which is patterned in a manner that the outsideshape portion of the piezoelectric oscillating piece is left, on thesubstrate surface, for the purpose of performing only etching of theoutside shape, and removing the metal film by etching;

continuing the shape formation of the piezoelectric oscillating piece bybringing the above-described substrate into contact with an etchingsolution to form the shape of the piezoelectric oscillating piece;

then, etching the side surface of the piezoelectric oscillating piece,forming an electrode on a piezoelectric oscillating piece for frequencyevaluation, which is cut out from the substrate, measuring theoscillation frequency, and conducting rough frequency adjustment byadjusting the etching amount of the side surface of the outside shapebased on the measurement result; and

then, forming the electrode patterns on the surfaces of allpiezoelectric oscillating pieces.

Further, in the method for manufacturing the piezoelectric resonatorincluding a base, a plurality of vibrating arms extending from the base,grooves formed in these respective vibrating arms, the present inventionincludes the steps of:

forming a metal film on the surface of the base which is a piezoelectricsubstrate;

patterning the surface of the metal film so that the outside shapeportion of the piezoelectric oscillating piece is left, forming a resistmask having apertures at the portions corresponding to the grooves ofthe vibrating arms, and removing the metal film by etching;

forming the grooves on the vibrating arms thereafter by bringing theabove-described substrate into contact with an etching solution, andforming the shape of the piezoelectric oscillating piece to the samedepth as the grooves;

thereafter, covering the aperture areas of the metal film opening at theportions corresponding to the grooves of the vibrating arm with themetal film;

next, continuing the shape formation of the piezoelectric oscillatingpiece by bringing the above-described substrate into contact with anetching solution to form the shape of the piezoelectric oscillatingpiece;

then, etching the side surface of the piezoelectric oscillating piece,forming an electrode on the piezoelectric oscillating piece forfrequency evaluation, which is cut out from the substrate, measuring theoscillation frequency, and conducting rough frequency adjustment byadjusting the etching amount of the side surface of the outside shapebased on the measurement result; and

then, forming the electrode patterns on the surfaces of allpiezoelectric oscillating pieces.

According to the present invention, etching to form the outside shape ofthe piezoelectric oscillating piece and etching to form the grooves areconducted simultaneously, and after forming the groove, the shapeformation of the piezoelectric oscillating piece is started again fromthe same depth as the grooves under the condition of covering thegrooves with the metal film. After the outside shape is formed, matchingof frequency is conducted by etching the side surface of thepiezoelectric oscillating piece in succession. Therefore, the matchingof frequency can be performed by processing only the side surface of thepiezoelectric oscillating piece. Accordingly, is compared with the usualpractice of conducting the frequency matching by processing the sidesurface of the piezoelectric oscillating piece and processing thegrooves formed in the vibrating arms at the same time, the roughfrequency adjustment can be achieved at a low etching rate. Therefore,it is possible to perform the frequency matching without unduedifficulty and with high accuracy. This makes it possible to get thepiezoelectric oscillating piece which has an easily adjustable range offrequency with high reliability when conducting the fine frequencyadjustment after forming the electrode pattern later.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an example of the tuning fork typequartz resonators relating to an embodiment of the present invention;

FIGS. 2A to 2E are schematic cross sectional views showing a method formanufacturing the tuning fork type quartz resonator relating to theembodiment of the present invention;

FIGS. 3F to 3J are schematic cross sectional views showing the methodfor manufacturing the tuning fork type quartz resonator relating to theembodiment of the present invention;

FIGS. 4K to 4O are schematic cross sectional views showing the methodfor manufacturing the tuning fork type quartz resonator relating to theembodiment of the present invention;

FIG. 5 is a plan view showing an example of the originals of the quartzoscillating piece manufactured in the manufacturing process of thetuning fork type quartz resonator relating to the embodiment of thepresent invention;

FIGS. 6A and 6B are a schematic vertical cross sectional view and a backview showing an example of quartz resonator packages which house thetuning fork type quartz resonator relating to an embodiment of thepresent invention;

FIG. 7 is a schematic plan view showing an example of the tuning forktype quartz resonators;

FIGS. 8A to 8E are schematic cross sectional views showing the methodfor manufacturing a conventional tuning fork type quartz resonator; and

FIGS. 9F to 9I are schematic cross sectional views showing the methodfor manufacturing the conventional tuning fork type quartz resonator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

A method for manufacturing a tuning fork type quartz resonator which isa piezoelectric resonator will be explained as an embodiment of thepresent invention. Since the structure of the quartz resonator relatingto the present embodiment is the same as that of the quartz resonatorexplained in the article of Related Art with reference to FIG. 7,explanation of the same portions will be omitted.

As shown in FIG. 1, a first excitation electrode 41 is formed on thewhole inner surfaces of a plurality of grooves aligned in thelongitudinal direction of an vibrating arm 2 a, for instance, a firstgroove 31 and a second groove 32, and between these grooves 31 and 32 onthe vibrating arm 2 a out of the vibrating arms 2. That is, by theexcitation electrode 41 formed on a so-called bridge portion 43corresponding to a portion between the first groove 31 and the secondgroove 32, the excitation electrodes 41 within the respective grooves 31and 32 of the vibrating arm 2 a are connected to each other. The secondexcitation electrode 51 is formed on both side surfaces 21, 21 of thevibrating arm 2 a and the tip portions of the main surfaces 22, 22 (thefront side and the back side). Furthermore, on the tip portion of thevibrating arm 2 a, an adjusting weight 50 which is a metal film foradjusting the oscillation frequency by adjusting the weight isinstalled. The adjusting weight 50 is a part of the excitation electrode51, but the film thickness and materials for the electrode etc. aredifferent from electrodes on other portions. It should be noted that theexcitation electrodes 41 and 51 in FIG. 1 are expressed using slantlines and black dots to make the drawing of both electrodes easier tosee. Accordingly, the slant lines in FIG. 1 are not for showing a crosssection of the quartz piece.

A second excitation electrode 51 is formed on the whole inner surfacesof a plurality of grooves aligned in the longitudinal direction of anvibrating arm 2 b, for instance, a first groove 31 and a second groove32, and between each of these grooves 31 and 32 on the vibrating arm 2 bout of the vibrating arms 2. The first excitation electrode 41 is formedon both side surfaces 21, 21 of the vibrating arm 2 b and the tipportions of the main surfaces 22, 22 (the front side and the back side).It should be noted that even on the tip portion of the vibrating arm 2b, an adjusting weight 40 for adjusting the oscillation frequency byadjusting the weight is installed in the similar manner. The arrangementof electrodes provided on the vibrating arms 2 a and 2 b are the same aseach other except that the excitation electrodes 41 and 51 are reversed.An electrode pattern made of a derivation electrode 42 is formed on thesurface of a base 1 so that these first excitation electrodes 41 areelectrically connected to each other. An electrode pattern made of aderivation electrode 52 is formed on the surface of the base 1 so thatthe second excitation electrodes 51 are electrically connected.

A method for manufacturing the quartz resonator shown in FIG. 1 will beexplained referring to FIG. 2A to FIG. 4O. Though a large number ofquartz resonators can be obtained from a sheet of piezoelectricsubstrate, FIG. 2A to FIG. 4O are views which explain one piece of thequartz resonator made at a certain portion of a sheet of thepiezoelectric substrate. FIG. 2A to FIG. 4O are views showingmanufacturing processes for a cross sectional portion along B-B line inFIG. 1. First, after polishing and cleaning a quartz wafer 60 which is acut out substrate, a metal film 61 is formed by a sputtering method(FIG. 2A). A film in which gold (Au) is stacked on a backing film of,for instance, chromium (Cr) is used as the metal film 61.

Then, after applying photoresist on such a metal film 61 by a spraymethod for instance (FIG. 2B), the photoresist is exposed and developedto form a tuning fork shaped resist film 62 having an aperture 45 atportions corresponding to the above-described grooves 31 and 32 (FIG.2C). Thereafter, the quartz wafer 60 is immersed in a potassium iodidesolution (KI) using the resist film 62 as a mask to perform wet etching.Thereby, a portion of the metal film 61 not covered by the resist film62 is removed (FIG. 2D).

Then, the quartz wafer 60 is immersed in hydrofluoric acid that is anetching solution to perform wet etching so that the grooves 31 and 32 ofthe vibrating arms 2 a and 2 b shown in FIG. 1 are formed and theoutside shape of a quartz piece 65 is formed to the same depth as thegrooves 31 and 32 (FIG. 2E). Next, after all of the metal film 61remaining on the surface of the quartz wafer 60 is peeled off, a newmetal film 63 is formed on the surface of the quartz wafer 60 by thesputtering method in the same way (FIG. 3F).

Next, after applying photoresist on the surface of the quartz wafer 60by the spray method for instance (FIG. 3G), the photoresist is exposedand developed in a manner so as to obtain a pattern having the shape ofthe quartz piece, namely, a tuning fork shape pattern, so that a tuningfork shaped resist film 64 is formed (FIG. 3H). Wet etching is conductedby immersing the quartz wafer 60 into a potassium iodide solution and aportion of the metal film 63 not covered with the resist film 64 isremoved (FIG. 3I).

Thereafter, wet etching is conducted by immersing the quartz wafer 60into hydrofluoric acid that is an etching solution so that thecontinuation of the outside shape formation of the quartz piece 65 isconducted from the same depth as the grooves 31 and 32. After formingthe outside shape of the quartz piece 65, rough frequency adjustment isconducted by etching the side surface of the outside shape of the quartzpiece 65 consecutively (FIG. 3J).

The rough frequency adjustment is conducted in the following manner. Thequartz wafer 60 is immersed into hydrofluoric acid first, and the wetetching is suspended when a predetermined period of time has passed. Onepiece of the quartz piece 65 for evaluating frequency is cut out from anoriginal 6 in which the electrode pattern shown in FIG. 5 has not formedyet and an electrode is formed on the quartz piece 65. Then, aprescribed voltage is applied to the electrode and an oscillationfrequency f is detected to determine whether or not the oscillationfrequency f is within a predetermined frequency. At this time, if theoscillation frequency f is not within the range of a predetermined rangeof frequency, the quartz wafer 60 is further immersed into hydrofluoricacid to conduct the wet etching. When a predetermined period of time haspassed, the wet etching is suspended, and one piece of the quartz piece65 for evaluating the frequency is cut out from the original 6 in whichthe electrode pattern has not formed yet similarly. An electrode isformed on this piece of the quartz piece 65, and a predetermined voltageis applied to the electrode and the oscillation frequency f is detectedto determine whether or not the oscillation frequency f is within thepredetermined range of the frequency. Thus, by minutely adjusting thetime for the etching of the quartz wafer 60 with hydrofluoric acid, thefrequency matching is performed. Thereafter, the metal film 63 remainingon the quartz wafer 60 is removed.

A process to prepare an electrode pattern will be explained next.Firstly, a metal film 71 to be an electrode is formed on both surfacesof the original 6 by the sputtering method (FIG. 4K). A film in whichgold (Au) is stacked on a backing film of, for instance, chromium (Cr)is used as the metal film 71.

Then, photoresist is applied to such a metal film 71 by a spray method(FIG. 4L). A resist film 72 excepting that corresponds to an electrodepattern is peeled off by photolithography(FIG. 4M). Thereafter, themetal film 71 at the portion where the resist film 72 has been peeledoff is etched to form the electrode pattern (FIG. 4N). Then, all of theresist film 72 remaining on the original 6 is peeled out (FIG. 4O).Then, the quartz resonator shown in FIG. 1 is to be cut out from theoriginal 6, in which the electrode pattern is formed.

In the above-described embodiment, etching for forming the outside shapeof the quartz piece 65 and etching for forming the grooves 31 and 32 areconducted simultaneously, and after the formation of the grooves 31 and32, the shape formation of the quartz piece 65 is started again from thesame depth as the grooves 31 and 32 in a state of covering the grooves31 and 32 with the metal film 63. Then after the shape formation, thefrequency matching is conducted by etching the side surface of thequartz piece 65 in succession. Accordingly, it is possible to performthe frequency matching by processing only the side surface of the quartzpiece 65. Accordingly, compared with the usual practice of conductingthe frequency matching by processing the side surface of the quartzpiece and processing the grooves formed in the vibrating arms at thesame time, the frequency matching can be achieved at a low etching rate.Therefore, it is possible to perform the frequency matching withoutundue difficulty and with high accuracy. This makes it possible to getthe piezoelectric oscillating piece having easily adjustable range offrequency with high reliability when conducting the fine frequencyadjustment after forming the electrode pattern later.

Furthermore, according to the above-described embodiment, the outsideshape of the quartz piece 65 and the grooves 31 and 32 are formedsimultaneously, and in the middle of the process, the grooves 31 and 32are covered with the metal film 63, while the outside shape etching ofthe quartz piece 65 is continued. Therefore, the manufacturing processof the quartz resonator is simplified with no complication and reductionof the manufacturing process can be realized.

In the above-described embodiment, the metal film 63 is formed in thegrooves 31 and 32 of the vibrating arms 2 a and 2 b as shown in FIG. 3Ithrough the manufacturing process shown in FIG. 3F to FIG. 3H. However,it is also possible that after the process shown in FIG. 2E, a maskhaving a plurality of holes of the same size as the grooves 31 and 32formed in the quartz wafer 60 is used, and the mask is positioned on theupper side of the quartz wafer 60 in a way that the holes of the maskand the grooves 31 and 32 formed in the quartz wafer 60 are respectivelylaid on top of one another so that the metal film 63 is directly formedonly on the grooves 31 and 32 of the vibrating arms 2 a and 2 b via themask. This mask is provided with a groove-shaped hole by chemicaletching or press processing on a thin plate made of stainless steel orthe like.

In addition, the above-described quartz resonator is housed in a package7 made of Surface Mounted Device (SMD) structure ceramics as shown in,for instance, FIGS. 6A and 6B. The package 7 is composed of a case 7 amade of, for instance, ceramics, of which the upper surface has anaperture, and a lid 7 b made of, for instance, metal. The case 7 a andthe lid 7 b are seam welded via a sealant 7 c made from, for instance, awelding material, and the inside thereof is in a vacuum state. In theinside of the above-described package 7, the base 1 of the quartzresonator 70 is fixed to a pedestal 71 via a conductive adhesive 7 d.The posture of the quartz resonator 70 in the above-described package 7is horizontal as such that the vibrating arms 2 a and 2 b are extendinginto a space on the inside of the package 7. On the surface of thepedestal 71, conductive paths 72 and 73 (73 is a conductive patharranged at right angle to the drawing) are placed, and the derivationelectrodes 42 and 52 formed on the base 1 are connected to theconductive paths 72 and 73 via the conductive adhesive 7 d. Theabove-described conductive paths 72 and 73 are connected respectively toelectrodes 74 and 75 arranged in a manner to oppose to the longitudinaldirection of the outside bottom surface of the case 7 a. As a result,the above-described quartz resonator 70 is forced to oscillate when avoltage is applied to the derivation electrodes 42 and 52 of the base 1via the electrodes 74, 75, the conductive paths 72, 73, and theconductive adhesive 7 d. Thus, a package type quartz resonator isstructured. The quartz resonator is installed on a wiring substrate (notshown) on which the circuit part of an oscillation circuit is installed,and thereby electric parts are structured.

1. A method for manufacturing a piezoelectric resonator including abase, a plurality of vibrating arms extending from the base, groovesformed in these respective vibrating arms, comprising the steps of:forming a metal film on the surface of the base which is a piezoelectricsubstrate; patterning the surface of the metal film so that the outsideshape portion of the piezoelectric oscillating piece is left, forming aresist mask having apertures at the portions corresponding to thegrooves of the vibrating arms, and removing the metal film by etching;forming the grooves on the vibrating arms thereafter by bringing thesaid substrate into contact with an etching solution, and forming theshape of the piezoelectric oscillating piece to the same depth as saidgrooves; thereafter, peeling off all of the metal film remaining on thesubstrate surface; then forming a metal film on the substrate surface;forming a resist mask which is patterned in a manner that the outsideshape portion of the piezoelectric oscillating piece is left, on thesubstrate surface, for the purpose of performing only etching of theoutside shape, and removing the metal film by etching; continuing theshape formation of the piezoelectric oscillating piece by bringing saidsubstrate into contact with an etching solution to form the shape of thepiezoelectric oscillating piece; then, etching the side surface of thepiezoelectric oscillating piece, forming an electrode on a piezoelectricoscillating piece for frequency evaluation, which is cut out from thesubstrate, measuring the oscillation frequency, and conducting roughfrequency adjustment by adjusting the etching amount of the side surfaceof the outside shape based on the measurement result; and then, formingthe electrode patterns on the surfaces of all piezoelectric oscillatingpieces.
 2. A method for manufacturing a piezoelectric resonatorincluding a base, a plurality of vibrating arms extending from the base,grooves formed in these respective vibrating arms, comprising the stepsof: forming a metal film on the surface of the base which is apiezoelectric substrate; patterning the surface of the metal film sothat the outside shape portion of the piezoelectric oscillating piece isleft, forming a resist mask having apertures at the portionscorresponding to the grooves of the vibrating arms, and removing themetal film by etching; forming the grooves on the vibrating armsthereafter by bringing said substrate into contact with an etchingsolution, and forming the shape of the piezoelectric oscillating pieceto the same depth as said grooves; thereafter, covering the apertureareas of the metal film opening at the portions corresponding to thegrooves of the vibrating arm with the metal film; next, continuing theshape formation of the piezoelectric oscillating piece by bringing saidsubstrate into contact with an etching solution to form the shape of thepiezoelectric oscillating piece; then, etching the side surface of thepiezoelectric oscillating piece, forming an electrode on a piezoelectricoscillating piece for frequency evaluation, which is cut out from thesubstrate, measuring the oscillation frequency, and conducting roughfrequency adjustment by adjusting the etching amount of the side surfaceof the outside shape based on the measurement result; and then, formingthe electrode patterns on the surfaces of all piezoelectric oscillatingpieces.